The board foot formula
A board foot is a piece 1 inch thick, 12 inches wide and 1 foot long: 144 cubic inches. For any board, multiply thickness (in) × width (in) × length (ft) and divide by 12. Multiply by the number of pieces.
| Board | Formula | Board feet |
|---|---|---|
| 1 × 12, 1 ft | 1 × 12 × 1 ÷ 12 | 1 |
| 1 × 6, 8 ft | 1 × 6 × 8 ÷ 12 | 4 |
| 2 × 4, 8 ft | 2 × 4 × 8 ÷ 12 | 5 1/3 |
| 2 × 6, 10 ft | 2 × 6 × 10 ÷ 12 | 10 |
| 4/4 hardwood, 6 in wide, 10 ft | 1 × 6 × 10 ÷ 12 | 5 |
Nominal or actual size?
Lumber yards price softwood dimensional lumber by its nominal size: a 2×4 is billed as 2 × 4 in, even though it measures about 1 1/2 × 3 1/2 in. Hardwood sold in quarters (4/4, 8/4) is priced by its rough thickness before planing. Use the size your yard bills by, or the result will not match the invoice.
Buying sheet goods too? The cut list optimizer tells you how many sheets of plywood or MDF a project needs.
Questions
How many board feet are in a 2×4×8?
5 1/3 board feet: 2 × 4 × 8 ÷ 12 = 5.33, using the nominal size.
How do I convert board feet to cubic metres?
One board foot is about 0.00236 m³, so 424 board feet make one cubic metre. The calculator shows both.
Should I add extra for waste?
For rough hardwood, add 15 to 30% for defects and milling; for dimensional lumber, a spare piece is usually enough.